Polyphenylene sulfide (PPS) is a specific type of polyarylene sulfide (PAS) thermoplastic resin that has excellent solvent, chemical, and heat resistance. It also possesses high strength and stiffness and low elongation at yield and break. PPS is often further compounded with glass and minerals for further increasing its strength and stiffness. Since PPS is highly rigid, it is often blended with an elastomeric impact modifier to improve flexibility. However, upon modification with an impact modifier, the chemical resistance of PPS is compromised. Since PPS is melt processed at a temperature of over 280° C., the high processing temperature often destroys the elastomeric character of the impact modifier. In some cases, higher processing temperature introduces undesirable processing attributes that are related to the low thermal tolerances of many elastomeric modifiers. These undesirable attributes may be aggravated if the elastomeric modifier is functionalized and may cause gelation during the processing which can lead to surface defects in the formed articles made therewith.
U.S. Pat. No. 4,889,893 discloses a two-component PPS composition that contains an olefinic copolymer containing 60 to 99.5% of an alpha-olefin and 0.5 to 40% by weight of a glycidyl ester of an alpha, beta-unsaturated carboxylic acid. One example of the olefinic copolymer is the copolymer of ethylene and glycidyl methacrylate. The functionalized elastomer is fairly effective in improving the impact strength of PPS. However, the olefinic nature of the modifier makes it somewhat less suitable for chemical media transport applications, particularly under conditions of very high temperature. Also, since the modifier has epoxy functionality, at high temperatures, the unreacted epoxy functionality tends to self-associate and causes surface blemishes or imperfections or gels on the pipe and tube articles made therefrom.
U.S. Pat. No. 6,608,136 discloses a polyphenylene sulfide alloy composition for wire and cables that comprises 40 to 90% by weight of PPS, about 1 to about 20% of an ethylene based grafting agent with grafting groups selected from unsaturated epoxide, unsaturated isocyanate, silane, or an oxazoline, and another ethylene copolymer with carboxylic acid containing groups. Whereas some improvement in elongation in break is possible by using the two co-grafting ethylene elastomers, there is a need for an improved composition that has lower swelling in fuel media and will process better under conditions of elevated temperatures. Ethylene based elastomers have limitations for providing adequate high temperature resistance under conditions of fuel transport.
U.S. Pat. No. 6,889,719 discloses a multilayer pipe for liquid antifreeze transport that has the inner layer made of resin material having a PPS resin that may optionally contain 20 to 40% by weight of a softening material from ethylene-glycidyl methacrylate (EGMA) and ethylene-propylene copolymers. Since the modifiers are polyolefin based, such a composition has limitations for use in fuel transport under processing temperatures of elevated temperatures. Also, the EGMA based elastomer has a tendency to self associate under PPS processing conditions.
European Patent Application 435024 (A3) discloses use of hydrogenated nitrile rubber (HNBR) for impact modification of PPS. The fuel resistance of HNBR is good, however, the notched izod impact property is not adequate. Furthermore, there is need for further improvement or reduction of the swelling of the PPS composition under conditions of elevated temperatures.
Therefore, there is a need for a flexible PPS composition that has a good balance of flexibility, impact properties, processability, and good solvent resistance. There is a need for more robust and flexible PPS compositions that largely retain the high temperature chemical resistance of PPS and still have enough flexibility for utilization in making defect-free tubes and pipes for chemical media transport.